Grunt task to remove unnecessary static files after compression

As we removed deletion of unnecessary files from iso build script
due to errors, many users were confused as they were trying to
change static files on a master node and there was no effect as
require.js compiles concatenates all the files into main.js. So we
decided to revive this functionality as a part of 'grunt build'

Change-Id: I227616153effcd7ded0ad6617773f46359443b4e
Merge "Grunt task to remove unnecessary static files after compression"